Robert Copperwhite

Photo-patternable hybrid ionogels for electrochromic applications

This work describes the development of photopatternable ionogels based on a hybrid organic/inorganic sol–gel material and both phosphonium (trihexyltetradecylphosphonium dicyanamide [P6,6,6,14][dca], trihexyltetradecylphosphonium bis(trifluoromethanesulfonyl)-amide [P6,6,6,14][NTf2]) and imidazolium (1-ethyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate [emIm][FAP]) room temperature ionic liquids (RTILs). Ionogels were prepared via a two step process with the RTIL content varied between 40 and 80 w/w%, and characterised via Raman and Electrochemical Impedance Spectroscopy. 1 and 2 photon polymerisation was performed on the hybrid ionogels using photolithography, resulting in three dimensional structures that were characterised using scanning electron microscopy. Electrochromic ionogels were prepared by addition of ethyl viologen dibromide (EV) to an ionogel containing [emIm][FAP] and hybrid sol–gel material. This composition was photo-polymerised on ITO electrodes by UV irradiation and subsequentially characterised viaUV/Vis spectroelectrochemistry. It was also possible to fabricate a solid state electrochromic device based on EV and switch between the colourless (oxidised) and blue (reduced) forms using a perturbation signal of 1 V.

Graphene-doped photo-patternable ionogels: tuning of conductivity and mechanical stability of 3D microstructures

This work reports for the first time the development of enhanced-conductivity, graphene-doped photo-patternable hybrid organic-inorganic ionogels and the effect of the subsequent materials condensation on the conductivity and mechanical stability of three-dimensional microstructures fabricated by multi-photon polymerisation (MPP). Ionogels were based on photocurable silicon/zirconium hybrid sol–gel materials and phosphonium (trihexyltetradecylphosphonium dicyanamide) [P6,6,6,14][DCA] ionic liquid (IL). To optimise the dispersion of graphene within the ionogel matrices, aqueous solutions of graphene were prepared, as opposed to the conventional graphene powder approach, and employed as catalysts of hydrolysis and condensation reactions occurring in the sol–gel process. Ionogels were prepared via a two step process by varying the hydrolysis degree from 25 to 50%, IL content between 0–50 w/w%, and the inorganic modifier (zirconate complex) concentration from 30 to 60 mol.% against the photocurable ormosil and they were characterised via Raman, Electrochemical Impedance Spectroscopy and Transmission Electron Microscopy. MPP was performed on the hybrid ionogels, resulting in three-dimensional microstructures that were characterised using scanning electron microscopy. It is clearly demonstrated that the molecular formulation of the ionogels, including the concentration of graphene and the zirconate network modifier, plays a critical role in the conductivity of the ionogels and influences the resulting mechanical stability of the fabricated three-dimensional microstructures. This work aims to establish for the first time the relationship between the molecular design and condensation of materials in the physico-chemistry and dynamic of ionogels.

A Camera Phone-Based UV-Dosimeter for Monitoring the Solar Disinfection (SODIS) of Water

In this letter, we report on the development of a novel camera phone-based UV-dosimeter for monitoring the solar disinfection (SODIS) of water. The dosimeter consists of a UV indicator, methylene blue, dispersed in an ethylcellulose-based polymer matrix. To provide quantitative measurement of UV dose, we demonstrate the use of a camera phone to analyze dosimeter color change in response to UV exposure. The dosimeter response exhibits excellent agreement with a polynomial model (R2) >; 0.99) over the UV exposure range tested. A notable advantage of the dosimeter described here is that it can be deposited on a variety of substrates with the potential to be incorporated into water containers. It is envisaged that use of such a dosimeter in conjunction with mobile phone technology will enhance the use of SODIS thereby impacting significantly on the challenge of providing clean drinking water in developing regions of the world.

Thermo-optic switches using sol-gel processed hybrid materials

There is a clear need for low cost, high performance and large-scale production of photonic chips. Network development requires more interconnecting components. A flexible and low-cost process using good quality material is necessary. The sol-gel process is a chemical method to fabricate glasses at ambient pressure and moderate temperature. The resulting material properties can be tuned depending on the precursors used. Hybrid materials, mixing organic and inorganic parts, offer the advantages of polymer-like materials and glasses. We have developed sol-gel-processed integrated optical circuits using hybrid materials. We report on the development of active devices based on the thermo-optic effect. Thermo-optic coefficients as high as -2.10-4/°K have been measured in our materials. This enables the design of compact devices with low power consumption. Our goal is to utilise the thermo-optic effect in the development of integrated optical switches. The kHz response time of such switches makes them unsuitable for modulation applications, but they can be used for network protection, reconfiguration purposes in routing and multiplexing applications such as Code Division Multiplexing. New designs, based on multimode interference couplers (MMIC), have also been created. In this work we first describe the synthesis of the hybrid materials as well as the fabrication processes. Using the measured properties of the materials developed, we can simulate the optical and thermal properties of the target devices. The simulation results have been exploited to model and optimise a range of switch designs, including MMI-based 1xN switches. Finally, we report on the full characterisation of the different structures and devices created in terms of fabrication quality and optical and thermal response.

Characterisation of novel refractometric sensing systems

Simulations and experimental results for novel refractometric-sensing platforms are presented here. The first platform is based on a multi-mode interference coupler (MMIC) in which the top and sidewalls of the coupler are exposed to a humidity-sensing enrichment layer. Sensor operation is based on the creation of self-images of the input field into the coupler, at regular intervals along the coupler. This phenomenon is due to interference between the optical modes in MMICs. Changes in the refractive index of the sensing layer cause predictable shifts in the position of the output image, which in turn affects the amount of light coupled into the output waveguide. Sensitivity enhancement has been demonstrated by fabricating longer MMICs capturing higher-ranking self-images, which are shifted more than the first self-image. Consequently, more significant changes in the amount of light coupled to the output are observed for a given refractive index change. The second platform demonstrated is a Multi-Channel Directional Coupler sensor (MCDC). It differs from the MMIC in that the sensing region now consists of multiple single-mode waveguides, which are in close enough proximity to allow light to transfer between the waveguides. Sensitivity dependance on platform length has been investigated and compared with that of the MMIC. The devices have been fabricated by the direct laser writing process on UV curable hybrid sol-gel materials. Such materials allow implementation of planar technology enabling integration on a silicon substrate. Future applications of these platforms include chemical and bio-chemical sensing is the areas of process, environmental and bio-diagnostic monitoring.

Sensing Performance of a Refractometric Optical Sensor Platform Based on Multimode Interference Couplers

This paper focuses on characterization of the sensing performance of a refractometric sensing platform based on multimode interference couplers (MMICs). Platform fabrication exploited a low-cost process using photocurable organic-inorganic hybrid sol-gel materials which were structured to form optical waveguides by direct UV laser writing. The sensing principle is based upon the high sensitivity of the optical field distribution formed in the MMIC toward changes in the refractive index of its environment. Simulations demonstrated the importance of correctly specifying the length of the MMIC section and illustrated that longer platforms are more sensitive due to a greater shift in self-image position. To characterize sensing performance, a porous sol-gel humidity sensing enrichment layer was coated on the MMIC. Relative humidity was detected by the system with a resolution of 0.097%. Refractive index resolution of the platform was determined to be ~ 2 × 10-6 RIU , which is an analyte-independent value and illustrates the generic nature of this platform. As such, this platform has immense potential for future applications as a label-free and real-time biosensor platform.

Hybrid zirconium sol-gel thin films with high refractive index

We describe the synthesis of optical quality thin film materials with high refractive index, employing zirconium based hybrid sol-gel precursors. As the zirconium propoxide precursor is unstable in the presence of a strong nucleophilic agent such as water, two synthesis routes have been performed employing a chelating agent and an organosilane precursor to avoid the formation of any undesired ZrO2 agglomerates, leading to organo-zirconate complexes and silicato-zirconate copolymers, respectively. The prepared hybrid sol-gel materials were deposited by spin-coating to form a transparent thin film on silicon substrates, and heat treated at 100 °C for the final stabilisation of the layer. The effect of the two synthesis routes on the optical properties of zirconium based hybrid sol-gel material is discussed. It was found that the nature and concentration of the organosilane precursor can significantly affect the structural properties of the deposited films. A correlation was also demonstrated between the concentration of the organosilane precursor and the refractive index of the material. By reducing the concentration of organosilane precursor, high refractive index materials were obtained. Similar behaviour was observed for the materials synthesised via chelating agent. The synthesis employing an organosilane precursor produces films with higher refractive index. A maximum refractive index of 1.746 was measured at 635nm for the deposited thin films.